A regenerator is used in a thermal cycle machine to add and remove heat from the working fluid during different phases of the thermal cycle. Such regenerators must be capable of high heat transfer rates which typically suggests a high heat transfer area and low flow resistance to the working fluid.
Different types of regenerators are already available on the market. Typically such regenerators comprise metal screens, cylindrically wound wire gauze or 3D random fiber networks as e.g. described in JP1240760, JP2091463 and WO01/65099; or even short metal fibers as e.g. described in EP1341630.
A regenerator needs to have a very low thermal conductivity in the fluid flow direction; since one end of the regenerator is hot and the other end is cold. The regenerator also needs to have very high thermal conductivity in the direction normal to the fluid flow so that the working fluid can rapidly adjust itself to the local temperature inside the regenerator. The regenerator must also have a very large surface area to improve the rate of heat movement with the working fluid. Finally, the regenerator must have a low loss flow path, for the working fluid, so that minimal pressure drop will result as the working fluid moves through. In case the regenerator is made of fibers, the regenerator must be fabricated in such a manner as to prohibit fiber migration as fragments might be entrained in the working fluid and transported to the compression or expansion cylinders and result in damage to the piston seals.
Accordingly, this invention seeks to provide a new regenerator and method of making such a regenerator, which embodies the properties indicated above. Furthermore, this invention seeks to provide a regenerator which can be fitted into a stirling engine, using a minimum of adjustment.